1. Field of the Invention
This invention relates to light sources based on semiconductors, semiconductor lasers or light-emitting diodes (LED) and, more particularly, to an improved power-supply system both for switching the source on or off and for operation in the steady state.
Several problems are involved in supplying power to semiconductor sources. In the steady state, it is necessary to provide the source with a power supply system comprising a regulating device to enable the power output of the source to be kept substantially constant. In addition, when the power supply system is switched on, it is necessary to provide a device which enables the source to arrive progressively at its operating state. Finally, when the source is switched on or off, the parasitic pulses emanating from the electronic circuits must not reach the source which is in danger of being damaged by the effect of these parasitic pulses.
Other precautions have to be taken for supplying power to semiconductor power lasers when these lasers are intended to operate in wide temperature ranges. Although it is known that a device for thermally regulating the laser by acting on its temperature by means of a frigatron can be used in arrangements such as these, a device of this type only provides for slow regulation.
Low-power lasers (below 5 mW) which operate at or around ambient temperature (i.e. at temperatures below 60.degree. C.) do not require thermal regulating devices because, at temperatures of this order, there is no risk of damage to the laser. Accordingly, it is possible to regulate the power emitted by the laser solely by varying the feed current.
2. Description of the Prior Art
Known of the prior art (thermal or electronic) comprise a photoelectric cell which supplied a signal characteristic of the variations in the power emitted by the laser by extracting part of the radiation emitted by the laser which is either a part of the radiation emitted frontwards in the propagation direction or the radiation emitted towards the rear of the semiconductor.